2000A&A...363..223W

The problem of confirming the youth of presumed zero-age main sequence (ZAMS) stars among field stars, i.e. outside of clusters and associations, is discussed within a statistical framework. A generic method to evaluate the completeness and contamination of samples is presented, criteria for the design of appropriate tests are outlined, and the performance of X-ray selection and the so-called `lithium test' is estimated. It is shown that for any test applied to this problem, the error of the second kind is far more important than the error of the first kind.